U.S. patent application number 11/829050 was filed with the patent office on 2008-01-31 for radical-enhanced atomic layer deposition system and method.
Invention is credited to William A. Barrow, Eric R. Dickey.
Application Number | 20080026162 11/829050 |
Document ID | / |
Family ID | 38997777 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080026162 |
Kind Code |
A1 |
Dickey; Eric R. ; et
al. |
January 31, 2008 |
RADICAL-ENHANCED ATOMIC LAYER DEPOSITION SYSTEM AND METHOD
Abstract
A radical-enhanced atomic layer deposition (REALD) system and
method involves moving a substrate along a circulating or
reciprocating transport path between zones that provide alternating
exposure to a precursor gas and a gaseous radical species. The
radical species may be generated in-situ within a reaction chamber
by an excitation source such as plasma generator or ultraviolet
radiation (UV), for example. The gaseous radical species is
maintained in a radicals zone within the reaction chamber while a
precursor gas is introduced into a precursor zone. The precursor
zone is spaced apart from the radicals zone to define a radical
deactivation zone therebetween. Purge gas flowing through the
various zones may provide flow and pressure conditions that
substantially prevent the precursor gas from flowing into the
radicals zone. In some embodiments, the system includes a partition
having one or more flow-restricting passageways though which the
substrate is transported.
Inventors: |
Dickey; Eric R.; (Portland,
OR) ; Barrow; William A.; (Beaverton, OR) |
Correspondence
Address: |
STOEL RIVES LLP
900 SW FIFTH AVENUE, SUITE 2600
PORTLAND
OR
97204-1268
US
|
Family ID: |
38997777 |
Appl. No.: |
11/829050 |
Filed: |
July 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60820785 |
Jul 29, 2006 |
|
|
|
Current U.S.
Class: |
427/569 ;
118/719; 427/255.28; 427/595; 428/450 |
Current CPC
Class: |
C23C 16/452 20130101;
C23C 16/545 20130101; C23C 16/45551 20130101 |
Class at
Publication: |
427/569 ;
118/719; 427/255.28; 427/595; 428/450 |
International
Class: |
B32B 15/04 20060101
B32B015/04; C23C 16/00 20060101 C23C016/00; C23C 16/48 20060101
C23C016/48; H05H 1/24 20060101 H05H001/24 |
Claims
1. A method for depositing a thin film on a substrate, comprising:
establishing a continuous flow of a purge gas through a reaction
chamber; maintaining a gaseous radical species in a radicals zone
within the reaction chamber while introducing a precursor gas into
a precursor zone within the reaction chamber, the precursor zone
being spaced apart from the radicals zone to define a radical
deactivation zone therebetween, the purge gas flowing through the
radicals zone, the deactivation zone, and the precursor zone such
that flow and pressure conditions within the reaction chamber
substantially prevent the precursor gas from flowing into the
radicals zone; and alternately transporting a substrate between the
radicals zone and the precursor zone repeatedly to thereby
alternately expose the substrate to the radical species and the
precursor gas multiple times, each exposure of the substrate to the
precursor gas resulting in some of the precursor gas adsorbing on
the substrate as an adsorbed precursor, and each subsequent
exposure of the substrate to the radical species resulting in some
of the radicals converting at least a portion of the adsorbed
precursor to an element or compound, whereby a thin film is formed
on the substrate.
2. The method of claim 1, wherein the purge gas is nonreactive with
the precursor gas.
3. The method of claim 1, wherein the radical species is generated
in-situ by applying energy to the purge gas in the vicinity of the
radicals zone.
4. The method of claim 3, wherein the radical species is generated
by exposing purge gas to UV light in the vicinity of the radicals
zone.
5. The method of claim 3, wherein the radical species is generated
by igniting a plasma from purge gas in the vicinity of the radicals
zone.
6. The method of claim 5, wherein the plasma is ignited by a DC
generator.
7. The method of claim 1, wherein the purge gas flows through the
reaction chamber along a flow path and the precursor zone is
located generally downstream in the flow path relative to the
radicals zone.
8. The method of claim 7, wherein the radical species are generated
by a radical generator that extends into the flow path and the
precursor gas is injected along a leeward side of the radical
generator.
9. The method of claim 1, wherein a continuous flow of the
precursor gas is injected into the precursor zone.
10. The method of claim 1, further comprising pumping from the
reaction chamber to create a vacuum therein.
11. The method of claim 1, wherein the transporting of the
substrate includes moving the substrate along a circular transport
path.
12. The method of claim 1, wherein the maintaining of the radical
species includes generating the radical species remotely of the
radicals zone and injecting the radical species into the radicals
zone.
13. The method of claim 1, wherein the radical species comprises
hydrogen radicals and the precursor gas comprises a
metal-containing molecule.
14. A device including a metal film formed by the method of claim
13.
15. The method of claim 1, further comprising contacting radicals
in the deactivation zone with a radicals deactivation device.
16. The method of claim 1, further comprising: introducing a second
precursor gas into the reaction chamber at a second precursor zone;
and transporting the substrate along a transport path that extends
into the second precursor zone.
17. The method of claim 1, further comprising maintaining a second
gaseous radical species within the reaction chamber.
18. The method of claim 1, wherein each exposure of the substrate
to the precursor gas results in self-limiting, saturating
adsorption of precursor gas on the substrate as adsorbed
precursor.
19. The method of claim 1, wherein the thin film is deposited by
atomic layer deposition.
20. The method of claim 1, wherein the thin film consists
essentially of a non-semiconductor material.
21. The method of claim 1, wherein the thin film consists
essentially of a metal.
22. A system for depositing a thin film on a substrate, comprising:
a reaction chamber, including an inlet for introducing a purge gas
into the reaction chamber and an outlet spaced apart from the
inlet, the outlet adapted to be coupled to a pump for pumping a
continuous flow of the purge gas through the reaction chamber along
a flow path from the inlet to the outlet; a radical generator
positioned along the flow path for maintaining a radical species in
a radicals zone within the reaction chamber; a precursor injector
spaced apart from the radical generator and located downstream in
the flow path of the purge gas relative to the radicals zone for
injecting a precursor into a precursor zone; a radical deactivation
zone interposed between the radicals zone and the precursor zone;
and a carriage for transporting a substrate between the radicals
zone and the precursor zone multiple times for alternately exposing
the substrate to the radical species and the precursor gas to
thereby deposit a thin film on the substrate.
23. The system of claim 22, wherein the radical generator extends
into the reaction chamber for generating radicals in-situ.
24. The system of claim 22, wherein the radical generator is
outside of the reaction chamber for generating radicals remotely of
the radicals zone.
25. The system of claim 22, wherein the radical generator includes
a plasma generator.
26. The system of claim 22, wherein the radical generator includes
a UV light source.
27. The system of claim 22, wherein: the carriage moves the
substrate along a transport path; and the radical generator
includes a containment shield extending from the wall of the
reaction chamber toward the transport path.
28. The system of claim 22, wherein: the radical generator projects
into the reaction chamber; and the precursor injector is positioned
in or adjacent a lee of the radical generator.
29. The system of claim 22, wherein the carriage includes a
rotating platen and a rotary feedthrough for driving the rotating
platen from outside of the reaction chamber.
30. The system of claim 22, wherein: the carriage moves the
substrate along a transport path; and the precursor injector
includes a wand that extends over and across the transport
path.
31. The system of claim 22, further comprising a radicals
deactivation device in the deactivation zone.
32. The system of claim 31, wherein the radicals deactivation
device is selected from the group consisting of: baffles, a getter,
a catalyst, a charged electrode, and combinations thereof.
33. The system of claim 22, further comprising a partition dividing
the reaction chamber between the radicals zone and the precursor
zone, the partition including at least one flow-restricting
passageway through which the substrate is transported by the
carriage.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(e) from U.S. Provisional Application No. 60/820,785, filed Jul.
29, 2006, which is incorporated herein by reference.
BACKGROUND
[0002] This disclosure relates to systems and methods for atomic
layer deposition (ALD) of thin films on a surface of a substrate
using radical species.
[0003] An overview of conventional ALD processes is provided in
Atomic Layer Epitaxy (T. Suntola and M. Simpson, eds., Blackie and
Son Ltd., Glasgow, 1990), which is incorporated herein by
reference. Numerous patents and publications describe the use of
radicals in connection with thin film deposition techniques,
including atomic layer deposition (ALD) and sequential chemical
vapor deposition. Many chemistries for radical-enhanced ALD (REALD)
have been proposed, and many more are expected to be developed in
view of the need for efficient production of high quality thin
films in semiconductor manufacturing and other industries. Of
particular interest are methods of forming non-semiconductor films,
such as pure metal films, for use in integrated circuits and for
other purposes. See, e.g., U.S. Pat. No. 6,616,986 B2 of Sherman
and U.S. Pat. No. 6,200,893 B1 of Sneh.
[0004] Radicals (also sometimes called "free radicals") are
unstable atomic or molecular species having an unpaired electron.
For example, hydrogen gas exists principally in diatomic molecular
form, but molecular hydrogen may be split into atomic hydrogen
radicals each having an unpaired electron. Many other radical
species are known. In embodiments described herein, the radicals
produced and used in the thin film deposition process may include
highly-reactive radical gas species formed of a single element such
as hydrogen, nitrogen, oxygen (e.g. ozone), or chlorine, as well as
compound radicals such as hydroxide (OH).
[0005] U.S. Provisional Patent Application No. 60/743,786, filed
Mar. 26, 2006 ("the '786 application"), and related U.S. patent
application Ser. No. 11/691,421, filed Mar. 26, 2007 ("the '421
application"), both titled "Atomic Layer Deposition System and
Method for Coating Flexible Substrates, are incorporated herein by
reference. The '786 and '421 applications describe systems and
methods for ALD in which a substrate such as a flexible web is
moved through two or more precursor chambers or zones separated by
an isolation chamber or zone to accomplish atomic layer deposition
of thin films on the surface of the substrate. As the substrate
traverses between the precursor zones, it passes through a series
of flow-restricting passageways of an isolation zone into which an
inert gas is injected to inhibit migration of precursor gases out
of the precursor zones. In the technique described in the '786 and
'421 applications, only the substrate gets coated and not the
reaction chamber walls or other parts of the system. The present
inventors have recognized that the processing system and method of
the '786 and '421 applications enables the use of UV light or
steady-state plasmas in one or more chambers to generate precursor
radicals, instead of requiring radicals to be cyclically introduced
into and removed from a common reaction chamber, as has previously
been proposed by Sherman, Sneh, and others.
[0006] The present inventors have also recognized that oscillating,
reciprocating, or circular movement of a substrate can be employed
to accomplish ALD processes using precursor radicals that are
continuously introduced into a reaction space by a steady-state
radical source. When the systems and methods described herein are
applied to accomplish thin film deposition processes with radicals,
there may be unique benefits and capabilities that are enabled.
[0007] Further aspects of various embodiments will be apparent from
the following detailed description, which proceeds with reference
to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic top view of a thin film deposition
system according to a first embodiment in which a circular
substrate platen is rotated to move one or more substrates through
multiple wedge-shaped precursor and purge zones or chambers;
[0009] FIG. 2 is a cross section elevation view of the system of
FIG. 1 taken along line 2-2 of FIG. 1;
[0010] FIG. 3 is a cross section elevation view of the system of
FIG. 1 taken along line 3-3 of FIG. 1;
[0011] FIG. 4 is a schematic top view of a cross-flow reactor for
thin film deposition according to a second embodiment;
[0012] FIG. 5 is a schematic elevation view of the cross-flow
reactor of FIG. 4; and
[0013] FIG. 6 is a schematic view of a web coating apparatus
according to a third embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0014] Described below are ALD methods and systems that involve
moving a substrate between zones that provide alternating exposure
to a chemical precursor and a radical species generated by an
excitation source (e.g., plasma, ultraviolet radiation (UV), high
temperature pre-heat with catalyst, etc.). In some embodiments, the
radicals are generated in-situ, i.e., within one of the zones in
the immediate vicinity of the substrate. While various system
configurations, geometries, and methodologies are envisioned for
providing the required substrate movement and precursor exposure,
example configurations shown in FIGS. 1-6 and serve to illustrate
some potential benefits of methods and systems according to the
present disclosure.
[0015] FIGS. 1-3 illustrate a radical-enhanced ALD (REALD) system
10 in accordance with a first embodiment. System 10 includes a
disc-shaped platter or carrier 14 that carries multiple substrates
20, illustrated as disc-shaped silicon wafers. Substrates of other
types and shapes may also be utilized. The substrate carrier 14
spins about its axis within a reaction chamber or process chamber
22 that is divided into several sub-chambers or zones 24, 26, 28,
and 30, such that the substrates 20 are transported along a
circular transport path sequentially through a first precursor zone
24, an intermediate "purge" zone 28, a second precursor zone 26,
and a further intermediate purge zone 28. In the embodiment
illustrated in FIGS. 1-3, exhaust zones 30 or buffer zones are
interposed between each of the precursor and purge zones 24, 26,
28.
[0016] First and second precursor chemicals (precursor 1 and
precursor 2) are introduced into the respective first and second
precursor zones 24 and 26 simultaneously, the two different
precursors being different chemicals. One of the precursor zones
(second zone 26 in FIG. 1) may include a radical generator 33
therein for generating a radical species from the second precursor
(precursor 2) in a radicals zone 32 within the precursor zone 26.
Alternatively, a purge gas may be introduced into second precursor
zone 26 and radicals may be generated from the purge gas. The purge
gas introduced in second precursor zone 26 may be the same as or
different from purge gas injected into one or more of the purge
zones 28. The purge gases used are preferably nonreactive with the
first precursor (precursor 1). In the embodiment illustrated, each
revolution of the substrate carrier 14 results in one full ALD
cycle. In alternative embodiments, a greater number of precursor
zones and intermediate purge zones may be included in the system 10
to achieve multiple ALD cycles from each revolution of the
substrate carrier 14.
[0017] In one embodiment, differential pumping and/or exhaust flow
control is utilized to generate pressure differentials between
certain adjacent zones to thereby prevent the first precursor
(precursor 1) from flowing from the first precursor zone 24 into
the second precursor zone 26. For example, first and second
precursor zones 24 and 26 are preferably operated at pressures that
are the same as or slightly lower than adjacent zones to help
inhibit precursors 1, 2 from leaking from precursor zones 24, 26.
Adjacent precursor and purge zones are separated by partitions 34,
with flow-restricting passageways 36 or slits provided in the
partitions 34 having slight clearance for substrates 20, so as to
inhibit migration of precursors from one precursor zone to the next
but to allow the carrier 14 to rotate and move the substrates 20
between the zones 24, 26, 28, 30. For simplicity, substrates 20 are
shown in FIGS. 1-3 sitting on top of a platen of carrier 14, but
may preferably be inset in pockets (not shown) in the platen, so as
to sit substantially flush with a top surface of the platen,
allowing improved flow-restriction to be achieved by sizing of
passageways 36 to provide only minimal clearance for rotation of
the platen. Exhaust zones 30 are preferably coupled to a vacuum
pump 40 (or multiple different vacuum pumps) to remove precursor
chemicals that may leak from precursor zones 24 and 26. Although
partitions 34 are illustrated as fins hanging down above the
carrier 14, they may also extend below the carrier 14 to prevent
mixing of precursors in the exhaust path, in which case multiple
exhaust lines may be employed with inline precursor reclamation
systems, as described in the '421 application. The purge zones 28
may be flooded with a non-reactive purge gas 42 at a higher
pressure than adjacent exhaust zones 30, providing a back-flow
condition to oppose gaseous precursors that have leaked into the
adjacent exhaust zones 30, thereby preventing precursors 1 and 2
from mixing in a common zone and reacting, except at the surface of
the substrate in an ALD reaction.
[0018] In one embodiment, the precursor and exhaust zones 24, 26,
30 are operated at a pressure in the range of 0.01 Torr to
approximately 10 Torr, with only slightly higher pressures being
maintained in the purge zones 28 by influx of purge gas 42 and/or
throttling of outlet passages from the purge zones 28. Operating
pressures lower than 0.01 Torr may require more complex vacuum
equipment and may not be effective to provide zone isolation by
differential pressure, particularly at pressures below which the
fluid continuum assumption ceases to apply. Operating pressures
higher than 10 Torr may be utilized in some embodiments, depending
on the precursor chemical(s) and radical species used in the thin
film deposition process. However, at operating pressures greater
than 100 Torr it may become more difficult to ignite a
radical-generating plasma utilizing a simple radio-frequency (RF)
plasma generator or direct-current (DC) plasma generator, and may
require a more expensive or less effective radicals generator
design. Also, at higher pressures, the mean free path of radicals
decreases, which increases the incidence of deactivating collisions
between radicals and may reduce substrate exposure rates for a
given distance between the radicals generator 33 and the substrate.
Thus, operating pressures in the low to medium vacuum range are
generally preferred over a higher pressure environment.
[0019] The passageways 36 may merely be slots cut in sheet metal
partitions; however, the partitions 34 are preferably made wider
than sheet metal in the direction of substrate travel. Partitions
34 define elongated flow-restricting passageways between process
zones which tend to inhibit inter-zone leakage and mixing of
precursors 1, 2. For example, the passageways 36 may be on the
order of the same width in the direction of travel as the chambers
of the various precursor and purge zones. FIG. 1 depicts
wedge-shaped partitions 34 and passageways 36 therethrough (FIGS.
2-3), but other shapes may also be suitable, depending on the
substrate path. For convenience and clarity of illustration, the
partitions 34 are shown in FIGS. 1-2 as being solid, but could also
be made hollow.
[0020] In the system illustrated, there are two differentially
pumped purge zones 28, with a substrate passing through one of the
purge zones 28 and a flanking pair of exhaust zones 30 after each
exposure to one of the first and second precursor chambers 24, 26.
In another embodiment (not shown), one or more of the purge and
exhaust zones 28, 30 may be omitted. For example,
cross-contamination of precursors may be prevented by maintaining a
higher pressure in purge zones 28, than in the precursor zones 24
and 26, inhibiting both precursor 1 and precursor 2 from escaping
their respective precursor zones.
[0021] Another approach to eliminating or reducing the number of
purge and evacuation zones used is to utilize a normally inert
purge gas for precursor 2 which is so unstable in its radicalized
form that the radicals recombine or otherwise deactivate before
they can escape the precursor chamber 26 or adjoining passageways
36, even without differential pressure or a backflow condition.
Upon deactivation, the radicals typically recombine to form a
molecule that is nonreactive with the first precursor. The
inventors have recognized that when a highly unstable radical
species is used to perform REALD, the purge and exhaust zones 28,
30 may be eliminated entirely if a greater pressure is maintained
in the second precursor zone 26 than the first precursor zone 24 so
that the non-radical precursor (precursor 1 in this example) is
effectively isolated or purged away from the radicals zone 32.
Thus, in a two-chamber system, a pressure differential between the
precursor zones 24, 26 generated through differential pumping or
injection may operate to prevent the non-radical precursor
(precursor 1) from flowing into the radicals zone 32 and causing
non-ALD reactions.
[0022] One example of such a highly unstable radical species is
atomic hydrogen, generated from hydrogen gas (H.sub.2). Hydrogen
gas may be safely handled and delivered to the second precursor
chamber 26 in the form of a nonflammable forming gas--a mixture of
approximately 4% hydrogen gas and the balance an inert gas such as
helium (He). In its non-radical gaseous form, hydrogen gas (or
forming gas) may serve as a purge gas. Hydrogen gas may also be
readily disassociated into atomic hydrogen radicals (H.sup.-)
through ignition of a plasma via radicals generator 33. Atomic
hydrogen radicals may be used to perform a step in ALD of metal
thin films according to process chemistries described by U.S. Pat.
Nos. 6,616,986 B2 of Sherman and 6,200,893 B1 of Sneh.
[0023] Although the embodiment of FIGS. 1-3 depicts a substrate
carrier supporting six substrates, alternative embodiments may
include substrate carriers that support a smaller or larger number
of substrates. For example, in one embodiment, a substrate carrier
holds a single substrate that is rotated about its central axis. In
still other embodiments, the substrate carrier may move the
substrate back and forth in a reciprocating translating manner or
in another movement pattern, so that substrates are moved between a
first precursor zone, a first purge zone, a second precursor zone,
and a second purge zone (which may or may not be the same as the
first purge zone), and perhaps also to one or more evacuation
zones.
[0024] The entire system 10 may be heated or merely the volume of
precursor zones 24 and 26 of the system may be heated.
Alternatively, the substrate itself may be heated instead or in
addition to the system 10 or precursor zones 24, 26. At least one
of the precursor zones 24 and 26 is a radicals zone 32 wherein
radicals are generated or introduced. The radicals may be generated
by any of many well known excitation sources, such as a plasma,
corona discharge, filament array, ultraviolet light, microwave
energy, radio-frequency (RF) energy, and direct current (DC) for
example. An excitation source 50 may include a power source 52
coupled to a radicals generator 33 positioned at least partially in
the radicals zone 32 for generating radicals in-situ. When an
optical source (not shown) is used for radicals generator 33, it
may be located just outside of radicals zone, beyond a window into
radicals zone 32 through which illumination is directed. In still
other embodiments (not shown) the radicals generator may be remote
from the radicals zone 32.
[0025] If the excitation source is remote from the radicals zone
32, remotely-generated radicals must be transported into the
radicals zone 32 so that a sufficient amount of the radicals reach
the surface of the substrate before recombining or otherwise
deactivating. U.S. Pat. No. 5,256,205 describes one method and
device utilizing a microwave cavity for generating a plasma to
disassociate a reagent gas into highly-reactive radicals, which are
then transported into a reaction chamber by a surrounding jet of
supersonic carrier gas. The radical generation and injection method
of the '205 patent may be useful for remote generation and delivery
of radicals in conjunction with the systems and method described
herein.
[0026] The excitation source 50 is preferably operated in a
continuous or steady-state manner, rather than being pulsed on and
off during each deposition cycle. In one embodiment, the radicals
are generated from the precursor present in the radicals zone 32.
In some embodiments, the radicals are generated from a purge gas
flowing through the radicals zone 32. Ions may also be generated
together with or instead of the radicals. An ion containment or
neutralizing device, such as a Faraday cage, may be used with the
radicals generator to inhibit ions from reaching the substrate. In
other embodiments, the radicals comprise radical ions. And in still
other embodiments, ions are generated for use in thin film forming
reactions instead of or in addition to radicals. For convenience,
chemicals from which radical species or ions are generated are
sometimes referred to herein as precursors, regardless of whether
any component thereof ultimately forms part of the thin film
deposited on the substrate.
[0027] Systems according to the present disclosure may expose to
precursors either one or both sides of flat substrates like
semiconductor wafers, depending on the shape and structure of the
substrate carrier, and whether the bottom side of the substrate is
masked by the carrier. Systems according to the present disclosure
may also be incorporated in or combined with other tools or
devices. For example, systems and methods disclosed herein by be
incorporated in so-called cluster tools for semiconductor
processing, wherein multiple process steps (such as deposition,
etch, planarization, etc.) are performed serially at a single
station or in adjacent stations managed by a centralized control
system. In a cluster tool implementation, systems for ALD according
to the present disclosure may have a substrate carrier sized to
hold and rotate or translate a single wafer, rather than the
multi-wafer platter shown in FIG. 1.
[0028] As mentioned above, systems according to the present
disclosure are not limited to rotating substrate carrier systems of
the kind shown in FIG. 1, but may also include carriage
configurations that provide for rotation, translation, or other
reciprocating or circulating motion of a substrate through or into
contact with multiple precursor zones. Movement of the substrate
may be accomplished without movement of a platter or other
platter-like carriage. For example, the substrate may be handled by
its edges as it is moved through processing zones of the system.
Examples include rotation of the substrates on a cylindrical
substrate carriage, a linear reciprocating system, and a flexible
substrate web coating system of the kind described in the '786 and
'421 applications (App. Nos. 60/743,786 and 11/691,421), which are
incorporated herein by reference. Advantageously, systems should be
designed to prevent free precursor (i.e. precursor that is not
adsorbed to the substrate surface) from one precursor zone from
reaching one or more of the other precursor zones, including the
radicals zone 32.
[0029] In some embodiments, the radicals of the radicals zone may
be deactivated prior to reaching the precursor zone by making the
path length between the radical and precursor zones sufficiently
long to allow deactivation to occur. On the other hand, the
throughput of the system is improved by moving the substrate as
quickly as possible and by spacing the precursor zones as closely
as possible, so the precursor zones should preferably be spaced no
farther apart than necessary to prevent non-ALD deposition.
Radicals may also be deactivated by "active deactivation device" or
means, such as the use of other vapor species which facilitate the
deactivation, or by the use of materials that would react with the
radicals to either trap or deactivate them, for example, a getter
or a catalyst for deactivation on some of the surfaces between the
radicals zone and the next precursor zone. Passive deactivation may
be accomplished by allowing sufficient distance between the
radicals zone and, optionally, by providing baffles along the zone
between the radicals zone and the precursor zone to increase
surface area for collisions.
[0030] By configuring the precursor zones 24 and 26 and
intermediate purge zones 28 so that non-surface bound radicals
cannot reach the precursor(s) and vice-versa, the excitation source
may remain activated in a stable, steady state during the entire
deposition sequence without undesirable consequences of the radical
mixing with the non-radical precursor in the reaction chamber.
Preventing such mixing may prevent partial or complete
decomposition of the non-radical precursor or precipitation of
reaction products. Thus, the systems described herein may also
prevent the accumulation of film along walls of the precursor
zones. Since there is no coating accumulation on the walls, nor
particularly on the excitation source or nearby surfaces,
excitation sources such as plasma sources may be made more stable
over the duration of many runs (each run comprising perhaps
thousands or tens of thousands of ALD cycles). Furthermore, optical
sources such as UV light sources may be used as steady-state
excitation sources because ALD coatings, which might otherwise
accumulate in a pulsed traveling wave ALD reactor, can be prevented
from depositing on optical windows to the radicals zone through
which such light sources are projected. The ease by which UV
sources and other optical excitation sources may be employed in
systems and methods of the present disclosure is expected to
facilitate metal deposition processes using ALD, as well as the
formation of oxides, nitrides, and other materials by ALD.
[0031] For cases where only the radical species is reactive with
the other precursor(s), isolation of the precursor zones to prevent
areas where they are simultaneously present, can be greatly
simplified. Inert gas flows and/or local pumping speeds may be
modulated in different areas of the overall chamber, to generate a
pressure gradient and a net flow of precursors and reaction
byproduct gasses away from the radical generation zone 32. The
radicals re-combine or are otherwise deactivated prior to reaching
the other precursor zone(s). For many desirable chemistry sets,
such as those that use hydrogen radicals, deactivation may be
accomplished passively by simply separating the zones by a distance
sufficient to allow the recombination of the radicals.
[0032] FIGS. 4 and 5 illustrate top and side schematic views of a
cross-flow REALD reactor system 100 in accordance with another
embodiment. With reference to FIGS. 4 and 5, system 100 includes a
reaction chamber 110 that bounds a reaction space 112. A purge gas
source 118 is coupled to the reaction chamber at an inlet 120 and a
vacuum pump 128 is coupled to an outlet 130 at the opposite end of
reaction chamber 110 from inlet 120 so as to provide a continuous
flow of purge gas along a flow path extending between inlet 120 and
outlet 130. Reaction space 112 may be elongated in the direction
from inlet 120 to outlet 130 so as to facilitate laminar flow or an
even flow distribution of purge gas across the reaction space 112
as the purge gas flows across processing zones. A radicals
generator 140 is positioned along a flow path of the purge gas for
exciting purge gas and generating radicals in a radicals zone 144
within reaction space 112. The reaction chamber 110 may be situated
inside of a surrounding pressure vessel (not shown) of an ALD
reactor, such as a Planar Systems P400A reactor, with process and
purge gases being supplied through the pressure vessel to reaction
chamber 110 via feedthroughs.
[0033] Radicals generator 140 may include of any of the types of
radicals generators described above with reference to FIGS. 1-3,
but may preferably be a DC or RF generator located along a top
panel or lid 146 of reaction chamber 110 for generating a plasma
and accompanying radicals in-situ. In another embodiment, the
radicals generator includes a UV light source. In addition to an
excitation device proximal of the reaction chamber lid 146,
radicals generator 140 may include a containment shield 148 or
curtain that projects away from lid 146 toward the substrate path
to help contain and maintain radicals in radicals zone 144.
Containment shield 148 may be formed of a non-conductive material,
such as polytetrafluoroethylene (PTFE) sold by DuPont Corporation
under the Teflon.RTM. brand, to prevent loss of ions.
Alternatively, containment shield 148 may be formed of an
electrically conductive material for reducing ions. A PTFE
containment shield 148 may comprise a cylinder that extends from a
plasma generator electrode to within 0.25 inch or less from the
substrate path. In an alternative embodiment (not shown), the
radicals generator 140 is located outside of the reaction chamber
for remote radical generation.
[0034] A source of precursor gas 150, such as a metal-containing
precursor gas is piped into reaction chamber 110 to a precursor
injector 152, where it is injected into the reaction space 112 at a
precursor zone 154 spaced apart from radicals generator 140 and
radicals zone 144. Precursor injector 152 is preferably positioned
generally downstream in the flow path of the purge gas relative to
radicals generator 140 and radicals zone 144, leaving a radical
deactivation zone 158 between the radicals zone 144 and the
precursor zone 154. In the embodiment illustrated, precursor
injector 152 is located directly downstream from radicals generator
140 along its leeward side. However, in other embodiments, radicals
generator 140 and precursor injector 152 may be staggered in the
flow path so that the precursor injector 152 is not directly in the
lee or wake of the radicals generator 140, but is still closer to
outlet 130 than radicals generator 140 (i.e., generally downstream
of radicals generator 140). In still another embodiment, precursor
injector 152 and radicals generator 140 may be located side-by-side
at the same distance from inlet and outlet, but spaced apart to
prevent the flow or migration of precursor gas into radicals zone
144. Precursor injector 152 may comprise a wand with holes along
its length, as illustrated in FIG. 5, which may extend across and
over the path followed by substrates 180. In alternative
embodiments, precursor injector 152 may include a showerhead type
injector or any other type of gas injector, but preferably one that
distributes gas across a desired processing zone.
[0035] As with the embodiments described above with reference to
FIGS. 1-3, the purge and precursor gases are preferably not
reactive with each other, except when the purge gas is radicalized.
The flow of purge gas through radicals zone 144, deactivation zone
158 and precursor zone 154 establishes pressure and flow conditions
within the reaction space 112 that substantially prevent precursor
gas from flowing into the radicals zone 144 and reacting with
radicals generated by radicals generator 140. And the distance
between the radicals zone 144 and the precursor zone 154 may also
allow radicals to be deactivated or otherwise cease to be present
in any substantial amount before reaching precursor zone 154, so
they will not react with the precursor gas. For example, hydrogen
radicals may deactivate over a distance as short as 1 mm under some
process pressure and temperature conditions, but under other
conditions may require 5 cm to 20 cm, or more, to deactivate.
Deactivation of oxygen or nitrogen radicals typically requires a
greater distance than for hydrogen, or the use of an active
deactivation device.
[0036] An active radicals deactivation device, such as a getter,
catalyst, reactive gas species, and/or a charged or grounded
electrode may be located in radical deactivation zone 158 to help
inhibit radicals from reaching precursor zone 154. In another
embodiment, a grid of conductive mesh may extend across radical
deactivation zone and be coupled to the conductive material of
reaction chamber 100 to form a Faraday cage around precursor zone
154. One radicals deactivation device, illustrated in FIG. 5,
includes a series of baffles 162 for enhancing deactivation in
radicals deactivation zone 158. Baffles 162 may comprise a series
of ridges along top lid 146 of reaction chamber 110 for increasing
the available surface area for collisions and by disturbing the
flow patterns, thereby increasing the likelihood of collisions
between radicals. Deactivation devices such as baffles 162 which
consume no outside energy or material are referred to herein as a
passive deactivation devices.
[0037] Again referring to FIGS. 4-5, system 100 includes a carriage
170 for transporting one or more substrates 180 along a transport
path between the radicals zone 144 and the precursor zone 154. Six
substrates are illustrated in FIGS. 4-5, but more or less could be
processed in different embodiments of the system. Carriage 170
preferably includes a rotating platen 184 that moves the substrate
alternately between the radicals zone 144 and the precursor zone
154 for alternately exposing each substrate 180 to the radicals and
precursor gases. Platen 184 is driven by a drive motor 186
preferably located outside reaction chamber 110 and the pressure
vessel (not shown) and coupled to platen 184 by a rotary
feedthrough 188.
[0038] In operation, one or more substrates 180 are loaded onto
platen 184 of carrier 170, then the reaction chamber 110 is sealed.
For example, in a semiconductor processing operation, wafer
substrates 180 may be loaded by a robotic wafer handling system
through a load lock (not shown) at a side of the reaction chamber
110. For example wafers may be loaded from a front-opening unified
pod (FOUP) by a robotic wafer loader. After the substrates 180 have
been loaded and the reaction chamber 110 closed, the reaction space
112 is then purged to remove unwanted gases. Reaction chamber 112
is then pumped via vacuum pump 128 to a desired operating pressure
and substrates 180 are heated by heaters (not shown) to a desired
operating temperature. Generally, low to medium vacuum pressures in
the range of 0.01 Torr to 100 Torr, and temperatures in the range
of 15.degree. C. to 400.degree. C. are suitable for REALD utilizing
the system and methods described herein. Higher temperatures may be
used, but are less desirable due to issues relating to mechanical
reliability of the deposition reactor and possible decomposition of
precursors leading to undesirable non-ALD CVD growth. Colder
temperatures may be used, but may be less desirable due to
condensation of low vapor pressure precursors on cold surfaces of
the reaction chamber or elsewhere in the system. In one embodiment,
the reaction chamber is brought to an operating pressure of
approximately 2 Torr and an operating temperature of approximately
150.degree. C. Other exemplary process conditions are described
below under the heading "Example". In other embodiments, process
chemistries may allow operating temperatures and pressures that are
much higher or lower. For example, some chemistries may be operable
at atmospheric pressure and temperature, and others at elevated
temperatures and/or pressures. During or after pump-down of
reaction space 112, a cleansing plasma may be generated and applied
to substrates 180 to remove contamination. After plasma cleansing,
the reaction space 112 may again be purged with an inert gas before
commencing REALD deposition cycles, as follows.
[0039] While maintaining the operating pressure and temperature, a
continuous flow of purge gas is introduced into the reaction
chamber 110 through inlet 120. Radical generator 140 is activated
to apply energy to and strike a plasma in the purge gas present in
radicals zone 144. The plasma is preferably kept ignited throughout
the following processing sequence, thereby maintaining a gaseous
radical species within the radicals zone 144. A precursor gas is
introduced into precursor zone 154 downstream from radicals zone
144 via precursor injector 152. The precursor gas is preferably
introduced in a continuous flow. The flow of purge gas from inlet
120 is desirably sufficient at the operating pressure to inhibit
the precursor gas from flowing into radicals zone 144 or otherwise
being swept or dragged into radicals zone 144 by movement of
carriage 170, except for precursor that has adsorbed to the surface
of the substrate 180 and carrier 170, as discussed below. The flow
of purge gas may establish, in the direction of purge gas flow, a
pressure differential between radicals zone 144 and precursor zone
154 that prevents migration of precursor gas from precursor zone
154 into radicals zone 144.
[0040] Carriage 170 transports substrates 180 alternately between
radicals zone 144 and precursor zone 154 to thereby alternately
expose substrate 180 to the radical species and the precursor gas
multiple times. In the embodiment illustrated, carriage 170
transports substrates 180 along a circular transport path. In other
embodiments, the transport path may be linear, elliptical, or
another shape, resulting from circulating or reciprocating motion
of substrates 180 between processing zones for alternating exposure
to radicals and precursor gases. The alternating exposures provide
the necessary processing conditions for ALD film growth. Each
exposure of a substrate 180 to the precursor gas results in some of
the precursor gas adsorbing to the substrate 180 as an adsorbed
precursor. Because the adsorption process may involve a chemical
transformation or reaction, the adsorbed precursor may be
chemically distinguishable from the precursor gas. In ALD
deposition, only a monolayer (a single atomic or molecular layer)
of adsorbed precursor will be present on the substrate, because the
precursor gas will not attach to or react with adsorbed precursor.
As used herein, the term "monolayer" includes imperfect monolayers,
wherein less than total coverage is achieved or some stacked or
dislocated regions result in slightly more than one continuous
atomic or molecular layer.
[0041] After an exposure of the substrate to the precursor gas in
precursor zone 154, translation of the substrate 180 results in a
subsequent exposure of substrate 180 to the radical species in
radicals zone 144. Exposure of substrate 180 to radicals zone 144
results in at least some of the radicals converting at least a
portion of the adsorbed precursor to another element (such as pure
metal) or another compound material. Of course, to achieve the
desired reaction, the radical generator 140 should be operated so
as to maintain a sufficient population of radicals at the surface
of the substrate 180 to achieve a desired ALD reaction (at least at
the location where substrate 180 is closest to the radicals
generator 140). In some chemistries, the radicals serve as a second
precursor such that the exposure to radicals results in a further
monolayer of an additional material forming through a chemical
reaction with the adsorbed (first) precursor. In other embodiments,
the radicals may facilitate an exchange reaction but are not
permanently incorporated in the thin film.
[0042] The circulating or reciprocating movement of substrate 180
returns substrate 180 to the precursor zone 154 via deactivation
zone 158. As described above, deactivation zone 158 serves as a
substantial barrier to the passage of free radicals to precursor
zone 154. Of course, the deactivation need not be perfect, and
trace radicals may pass to precursor zone 154, provided that they
do not frustrate ALD growth overall. Upon the return of substrate
180 to precursor zone 154, some of the precursor gas again adsorbs
to substrate 180, i.e., to the monolayer of thin film previously
coated, and the process repeats.
[0043] For characteristic ALD films to form, each sequential
exposure of substrate 180 to a precursor gas or radical species
should involve a self-limiting, theoretically saturating surface
reaction. And by preventing precursor gases and radical gases from
mixing in the reaction space, the reactions occur only at the
surface of the substrate, at available reaction sites.
Theoretically all or substantially all available reaction sites at
the surface of substrate 180 become occupied and the surface is
said to be saturated, terminating each reaction step. However, as
each reaction step proceeds to completion, the surface is converted
from being reactive to non-reactive as to the gaseous precursor or
radical involved in that step, and the reaction rate slows
exponentially over time according to the Langmuir principles of
molecule-surface reaction kinetics. The self-limiting reaction
kinetics of ALD and REALD both exhibit thin film deposition rates
that does not increase linearly with dosage increases. ALD and
REALD are therefore evidenced by a growth rate that is not linear
over time during a precursor exposure and that does not increase
linearly as a function of exposure dosage.
[0044] It is noted that the rate of movement of the substrate 180
by carriage 170 and the size of the process zones 144, 154 controls
the exposure times. Desirable exposure times may range from between
50 milliseconds (msec) and 100 msec in one embodiment operating at
2 Torr and 150.degree. C. and utilizing atomic hydrogen radicals.
However exposure times from 10 msec to 100 seconds may also be
utilized, depending on the operating temperature and pressure
within the reaction chamber 110, and the chemistry of the
deposition process. Desirable exposure times for a metal deposition
process utilizing hydrogen radicals may be achieved for 200 mm
wafers, a comparably sized precursor zone 154, and a comparably
sized radicals zone 144 using a rotating carriage 170 spinning at
approximately 90 rpm, for example. Similar results may be achieved
in a reciprocating carriage system (not shown) transporting
substrate 180 through processing zones at 2 meters per second
(m/s), for example.
[0045] The carriage 170 may also be driven to move one or more
substrates at variable rates, to achieve different exposure times
and movement rates at different locations along the transport path.
For example, substrate 180 may be moved quickly through the
radicals zone 144, and more slowly through the deactivation and/or
precursor zones 158, 154.
[0046] In the system of FIGS. 4-5 and for a substrate circulation
rate of 90 rpm, the cycle time for one complete REALD cycle is
approximately 0.67 second, resulting in deposition rates of between
approximately 50 angstroms per minute (.ANG./min) and 100
.ANG./min. Thus, using a 6-wafer rotating platen system, a
throughput of better than 1 wafer per minute may be achieved for
atomic layer deposition of thin films (such as a metal film) that
are at least 50 .ANG. thick, based on system platter load/unload
time of approximately 2 minutes, heat-up time of approximately 3
minutes, and deposition run time of approximately 1 minute.
[0047] In another embodiment (not shown) the radical and precursor
zones 144, 154 may be arranged side-by-side, with a longitudinal
partition (not shown) therebetween to prevent migration of
precursor gas from precursor zone 154 into radicals zone 144. In
this embodiment, carriage 170 moves substrates 180 through one or
more flow-restricting passageways in the partition.
[0048] In between each exposure to precursor gas and radicals,
reaction byproducts and excess precursor(s) continue to be pumped
out of the reaction chamber 110 by pump 128. Reaction byproducts
and precursor(s) are preferably nonreactive in the reaction space
112. For example, reaction byproducts of the self-limiting surface
reaction occurring in radicals zone 144 preferably do not react
with the precursor gas or with byproducts of the self-limiting
surface reaction taking place in precursor zone 154. Repeated
cycles of alternating precursor and radical exposure result in
deposition of a conformal thin film, preferably having typical ALD
qualities such as being pinhole free.
[0049] FIG. 6 shows a cross section elevation of a system 210 for
REALD deposition of a thin-film coating onto a flexible substrate
212 (shown in profile in FIG. 6), such as a web of plastic film or
metal foil, for example. With reference to FIG. 6, system 210
includes a precursor zone 214 and a radicals zone 216, separated by
an intermediate isolation zone 220 in which an inert fluid is
present. The inert fluid may comprise an inert liquid, but more
preferably consists essentially of an inert gas, such as nitrogen
(N.sub.2). When in use, a precursor gas is introduced into the
precursor zone 214 from a precursor delivery system 224. A second
precursor gas or a purge gas is introduced into radicals zone 216
from second precursor delivery system 226. Precursor delivery
systems 224, 226 may include precursor source containers (not
shown) located outside or within precursor and radicals zones 214,
216. Additionally or alternatively, precursor delivery systems 224,
226 may include piping, pumps, valves, tanks, and other associated
equipment for supplying precursor gases into precursor and radicals
zones 214, 216. An inert gas delivery system 228 is similarly
included for injecting inert gas into isolation zone 220. In some
embodiments, the same inert gas may be injected into isolation zone
220 and radicals zone 216.
[0050] Radicals may be formed in the radicals zone 216 by a
radicals generator 229 similar to any of those described above with
reference to FIGS. 1-5. Radicals generator 229 may preferably
continuously generate a population of a radical species
(illustrated by a cloud in FIG. 6) within radicals zone 216 by
means of a plasma, for example. In an alternative embodiment,
radicals generator 229 may be located outside of the chamber 246 to
generate radicals remotely for subsequent delivery into radicals
zone 216. As with other embodiments described herein, radicals
generator 229 may be operated in a continuous or steady-state mode
without incurring the penalties of plasma ramp times and build-up
of undesirable films on the radical generator 229 and walls of the
reaction chamber 230.
[0051] Precursor zone 214, radicals zone 216, and isolation zone
220 are bordered by an outer reaction chamber housing or vessel
230, divided by first and second dividers 234, 236 into three
sub-chambers, namely, a first precursor chamber 244, a second
precursor chamber 246 and an inert gas chamber 250. Vessel 230 may
comprise a pressure vessel or vacuum vessel substantially isolating
the process space from the external environment. In other
embodiments, the vessel 230 may have entrance and exit passageways
for interfacing with other process modules or equipment. A series
of first passageways 254 through first divider 234 are spaced apart
along a general direction of travel of substrate 212, and a
corresponding series of second passageways 256 are provided through
second divider 236. The passageways 254, 256 are arranged and
configured for substrate 212 to be threaded therethrough back and
forth between precursor and radicals zones 214, 216 multiple times,
and each time through isolation zone 220. For a web substrate,
passageways 254, 256 preferably comprise slits having a width
(exaggerated in FIG. 6) that is slightly greater than the thickness
of substrate 212 and a length (not shown) extending into the plane
of FIG. 6 (i.e., normal to the page) and that is slightly greater
than a width of the substrate 212. Isolation zone 220 is, thus,
preferably separated (albeit imperfectly) from precursor zone 214
by first divider 234 and from radicals zone 216 by second divider
236.
[0052] To substantially prevent non-ALD reactions caused by mixing
of non-adsorbed quantities of the precursor gas and radicals in one
of the chambers 244, 246, 250, the system 210 may inhibit the
migration of the precursor from precursor zone 214 into isolation
zone 220 and the migration of radicals from radicals zone 216 into
isolation zone 220. Passageways 254, 256 are preferably configured
to restrict the flow of gases between the zones 214, 216, 220, to
avoid or limit diffusion of precursor gases and radicals into a
common zone. Passageways 254, 256 may include slits sized only
slightly thicker and wider than the thickness and width of the
substrate 212 passing through them, leaving only a very small
amount of headroom and margins to allow substrate 212 to pass
therethrough without scraping against the sides of the passageways.
For example, headroom and margins may range between microns and
millimeters in certain embodiments. The passageways 254, 256 may
also include elongate tunnels through which the substrate 212
passes. Such slits and tunnels are sometimes referred to as slit
valves, although no actual moving valve gate is utilized.
Passageways 256 may be equipped with passive or active radicals
deactivation device, such as baffles or a catalyst, for example,
for further inhibiting radical species from escaping radicals zone
216. A radicals deactivation zone may extend from just beyond the
cloud of radicals shown in FIG. 6, to the uppermost end of
passageways 256.
[0053] In an alternate embodiment (not shown), the inert gas
chamber 250 of isolation zone 220 and dividers 234, 236 are
eliminated, so that isolation zone 220 essentially consists of a
series of long narrow passageways extending completely between
precursor zone 214 and radicals zone 216. In such an embodiment, no
common inert gas chamber 250 connects the passageways, so inert gas
is injected directly into the passageways medially of the precursor
zone 214 and radicals zone 216 to help prevent precursor migration
and mixing. Isolation zone 220 of this embodiment would include a
manifold, or a number of manifolds, for routing inert gas lines to
nozzles along the sides of the passageways. The manifold or
manifolds would be formed in the material of the reaction chamber
bordering the passageways, and may be connected to an inert gas
delivery system along the sides of the system, rather than at an
end of the system as shown in FIG. 6.
[0054] To help isolate the precursor gas from the radical species,
pressure differentials are preferably established between the
isolation zone 220 and the precursor zone 214 and between the
isolation zone 220 and the radicals zone 216. In one embodiment,
the pressure differentials may be generated by injecting inert gas
into isolation zone 220 at a pressure greater than the operating
pressure of the precursor and radicals zones 214, 216, and then
passively exhausting gases from the zones 214, 216. In another
embodiment, the exhaust from precursor and radicals zones 214, 216
could be controlled relative to a passive exhaust from isolation
zone 220 or by throttling an exhaust flow from isolation zone 220.
Pressure differentials may also be generated by pumping from
precursor zones via pump 258 or another source of suction.
Optionally, pump 258 may be coupled to all zones, with flow from
the various zones being controlled to maintain the pressure
differential. The migration of precursors from the precursor and
radicals zones 214, 216 into the isolation zone 220 may also be
prevented or limited by controlling both the relative flow rates of
gases into the zones and pumping speeds from the zones, through the
use of flow control valves, and other flow control devices. Flow
and pressure controls may be simplified through the use of highly
unstable radicals that tend not to persist long enough to escape
the second precursor chamber 246, in which case the pressure and
flows need be controlled only to prevent the precursor from
migrating from precursor zone 214 into radicals zone 216. A control
system (not shown) responsive to pressure sensors in the various
zones may also be utilized to control gas injection and exhaust
flow rates to help maintain a desired pressure differential.
[0055] In one example, isolation zone 220 operates at a pressure of
approximately 5 millitorr (i.e., the inert gas injection pressure
may be 5 millitorr), and pressure differentials of approximately
0.1 millitorr are maintained between isolation zone 220 and each of
the precursor and radicals zones 214, 216, so that an operating
pressure of approximately 4.9 millitorr is maintained in precursor
and radicals zones 214, 216 by way of suction applied to zones 214,
216 by pump 258. Lower and significantly higher pressure
differentials may also be used in some embodiments. The necessary
pressure differential will be affected by the geometry of
passageways 254, 256 (including height, width, and tunnel length,
if applicable), the headroom and margins around substrate 212
within passageways 254, 256, the transport speed of substrate 212,
the surface roughness of substrate 212 and passageways 254, 256,
and the location at which inert gas is injected, such as direct
injection into passageways 254, 256 or generally into inert gas
chamber 250. Other factors, such as operating temperature,
pressure, precursor species, and substrate type, may also affect
the amount of pressure differential necessary to inhibit or prevent
migration of precursor gases through passageways.
[0056] In some ALD processes, precursor gases having a very low
vapor pressure are utilized. To facilitate pumping and diffusion
control, an inert carrier gas may be mixed with such precursor
gases, either before or after introduction of the precursor gases
into the system 210, to control the pressure within zones 214,
216.
[0057] In some embodiments, it may be desirable to equalize the
pressures, or to deliberately mismatch the pressures in two or more
precursor zones to optimize growth conditions, or improve
utilization of precursor materials. It may also be desirable to
pump two or more of the zones separately, and introduce inert gas
into the precursor zones separately to further reduce zone
migration; for instance, a cross-flow condition may be used to flow
precursor in a direction orthogonal to the passageways 254, 256
(between first and second ends 272, 284). Inert gas may be
introduced locally within or near passageways 254, 256, to inhibit
gases from either adjacent zone from crossing through passageways
254, 256. If further isolation is necessary, multiple
differentially-pumped and purged zones may be used in series, with
flow-restricting passageways or wiper valve isolation between zones
and exhaust paths from each of the zones.
[0058] As described above, the precursor and radicals zones 214,
216 may be pumped to achieve an isolating pressure differential
between the isolation zone and the precursor zones. In one
configuration (not shown), separate pumps could be used for each of
the zones 214, 216, 220, preventing mixing of precursor gases in
the pump stack and the attendant growth of material or reaction
byproducts in any of the pumping lines, thereby preventing powder
and residue from accumulating and clogging the pump stack. Another
way to inhibit undesirable material deposits in the pump stack is
to trap exhaust precursors using a precursor trap 259, such as a
simple inline liquid nitrogen cooled trap. Similar precursor traps
may be placed in each of the precursor exhaust lines upstream of
their junction before the pump 258. By using inert gases and
precursor materials having different vapor pressures at a given
temperature, it may be possible to trap and reclaim up to
approximately 100% of exhaust precursor gases, while passing inert
gases to the pump stack. And because different precursors are not
mixed in the zones, the precursor purity is maintained, enabling up
to 100% utilization of precursor materials. Once filled, trap 259
may be replaced and the full trap 259 sent to another place for
precursor recovery. Alternatively, a filled trap 259 may be
converted into a precursor source by replacing the coolant in trap
259 with a heated liquid or by activating heating elements outside
trap 259. The particular operating temperature of trap/source would
depend on the precursor being trapped and its vapor pressure. A
liquid nitrogen trap, for example, may operate at lower than
100.degree. Kelvin. Other precursor traps and recovery/recycling
systems are described in detail in the '421 application, which is
incorporated herein by reference. Similar traps may be used with
the embodiments of FIGS. 1-6 described herein.
[0059] A substrate transport mechanism 260 of system 210 includes
multiple turning guides for guiding flexible substrate 212,
including a set of first turning guides 264 spaced apart along
precursor zone 214 and a second set of turning guides 266 spaced
apart along radicals zone 216. Turning guides 264, 266 cooperate to
define an undulating transport path of substrate 212 as it advances
through system 210. The substrate transport mechanism 260 may
include a payout spool 272 for paying out substrate 212 from a
first coil (input roll 274) for receipt at a first end 276 of
isolation zone 220, vessel 230, precursor zone 214, or radicals
zone 216. The substrate transport mechanism 260 may further include
a take-up spool 282 for receiving the coated substrate 212 from a
second end 284 of isolation zone 220, vessel 230, precursor zone
214, or radicals zone 216 opposite first end 276, and coiling the
substrate 212 into a take-up roll 286 or second coil. Payout spool
272 and/or take-up spool 282 may be located within vessel 230, such
as within isolation zone 220. Alternatively, payout and take-up
spools 272, 282 may be located outside of vessel 230, i.e., outside
of isolation zone 220, precursor zone 214, and radicals zone 216
(not shown).
[0060] Other embodiments of a web coating system are described in
the '786 and '421 applications, and can be readily modified to
include a radical generation device for utilizing methods according
to the present disclosure.
EXAMPLE
[0061] For ALD growth of cobalt (Co) thin film, equipment of FIGS.
4-5 may be employed as follows:
[0062] Substrate: silicon wafer, p-type (100);
[0063] Operating temperature of reaction space (i.e. substrate
temperature)=200.degree. C.;
[0064] Operating pressure of reaction space=1 Torr;
[0065] Purge gas: forming gas mixture of 4% hydrogen (H.sub.2) and
balance helium (He) at 100.degree. C. and flow rate of 1 standard
liter per minute (slm);
[0066] Precursor: dicobalt octacarbonyl (Co.sub.2(CO).sub.8)
delivered via a bubbler source at 25.degree. C. utilizing helium
(He) carrier gas at 10 standard cubic centimeters (sccm);
[0067] Radicals generator: in-situ DC plasma generator operating at
500 watts (or up to 1500 watts); and
[0068] Substrate rotation: 10 rpm.
[0069] Of course, many other process chemistries and processing
conditions may be employed. For example, the systems and methods
disclosed herein may be suitable for use with process chemistries
disclosed by Sherman (U.S. Pat. No. 6,616,986 B2) and Sneh (U.S.
Pat. No. 6,200,893 B1)
[0070] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments without departing from the underlying principles of the
invention. The scope of the present invention should, therefore, be
determined only by the following claims.
* * * * *